Scientists have unveiled a new hi-tech weapon to help combat the illegal trade of ivory in Africa: a map.

The map describes how the genetic profiles of African elephants vary across the continent, from the dense forests of western and central Africa to the vast eastern savanna.

The team behind the map, headed by Samuel Wasser, a biologist at the University of Washington in Seattle, says it can be used to verify where collections of ivory originated, by allowing police and customs officers to link stocks of tusks to herds known to live in a specific region.

It could also help alert officials to the emergence of poaching hotspots, where law enforcement needs to be bolstered.

Prof Wasser and his team visited sites in 16 African countries where most of the elephant population roams, and collected DNA from droppings and skin tissue. The DNA was analysed to identify key sequences of genetic code that distinguish one group of elephants from another.

Using a computer model, the team was then able to work out the likely genetic make-up of elephants in other parts of Africa and so build up a map of the elephants' genetic diversity.

Using the map, officials could ascertain the origin of tusks in national stockpiles or from intercepted consignments by simply taking DNA samples, a procedure that costs around £60, and checking them against the map. The team, whose work appears today in the Proceedings of the National Academy of Sciences, found that continent-wide the system could place half of all ivory within 300 miles of its origin, though accuracy varied from region to region, improving to within 84 miles in west Africa.

The map could have the biggest impact on poaching in African forests. While elephant numbers are easy to track in the open savannas, populations and poachers are tougher to monitor in the forests.

"My colleagues working in the forests are saying 'there are no elephants left here'," said Prof Wasser. "In the forest, you don't notice the change in population until it's so dramatic that it's almost too late to do anything about it."

The African elephant population dropped by 60% between 1979 and 1987, from 1.3m to 500,000, largely because of ivory poachers.

Although an international ban on ivory trading was passed in 1989, the three largest hauls of ivory, one of which amouned to around 6.5 tonnes, have occurred in the past two years.

In 2002, Botswana, Namibia and South Africa were granted permission to have one-off sales of legally acquired ivory. Next week, Namibia will petition the Convention on International Trade in Endangered Species and Wild Fauna and Flora to approve an annual quota of raw ivory sales of two tonnes a year.

Julian Blanc, of the World Conservation Union's African elephant specialist group in Nairobi, believes the genetic map could one day become a valuable tool in clamping down on the illegal trade of tusks.

He said: "Right now, it's probably not precise enough because it might not tell us if a consignment comes from one side of a national border or the other. But if it can be improved, it would be able to help verify whether ivory has been acquired legally and comes from the region they claim."